Non-Patent Literature 1, at chapter 22, defines a Self-Organizing Network (SON) technology for self-configuration and self-optimization of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN is a Long Term Evolution (LTE) radio access network. The SON technology defined in Chapter 22 of Non-Patent Literature 1 includes dynamic configuration of S1-MME and X2 interfaces, an Automatic Neighbour Relation (ANR) function, Mobility Load Balancing, and Mobility Robustness Optimization (MRO). The S1-MME interface (or S1-MME link) is a communication interface between an evolved NodeB (eNB) and a Mobility Management Entity (MME) located in a core network (i.e., Evolved Packet Core (EPC)). The X2 interface (or X2 link) is an inter-eNB communication interface. The eNB is an E-UTRAN/Long Term Evolution (LTE) base station. The MME is a control entity located in the core network (i.e., Evolved Packet Core (EPC)), and performs, for example, mobility management (e.g., location registration) of a User Equipment (UE), and bearer management (e.g., bearer establishment, bearer modification, bearer release). The UE is an E-UTRAN/LTE radio terminal (or mobile terminal).
The ANR function is one of the important features of the SON. An object of the ANR function is to release an operator from the burden of manually managing neighbour-cell relations (i.e., neighbour relations (NRs)). FIG. 1 shows a plurality of elements included in the ANR function disclosed in Non-Patent Literature 1. FIG. 2 shows a specific example of a neighbour relation table (NRT) disclosed in Non-Patent Literature 1.
As shown in FIG. 1, the ANR function resides in an evolved NodeB (eNB) and manages the conceptual NRT. The Neighbour Detection Function finds new neighbour cells, and adds NRs corresponding to the neighbour cells to the NRT. The Neighbour Removal Function removes unnecessary NRs from the NRT.
The NRT contains entries of all neighbour-cell relations (NRs) of cells controlled by the eNB. An NR in the context of the NRT is defined as a unidirectional cell-to-cell relation from a source cell to a target cell. As shown in FIG. 2, the NRT contains a Target Cell Identifier (TCI) to specify a target cell for each NR. When the target cell is an E-UTRAN cell, the TCI corresponds to the E-UTRAN Cell Global Identifier (ECGI) and Physical Cell Identity (PCI) of the target cell. The ECGI consists of a 3-byte Public Land Mobile Network Identity (PLMN ID) and 28-bit E-UTRAN Cell Identifier (ECI), and is used to specify the E-UTRAN cell globally uniquely. The PLMN ID is a unique identifier of a PLMN, and the ECI is a unique identifier of an E-UTRAN cell in a specific PLMN. The PCI is a number from 0 to 503 and distinguishes a cell from its immediate neighbour cells. In the PLMN, 504 (0 to 503) different PCIs are repeatedly used. That is, the PCI cannot uniquely specify a cell within a PLMN or globally.
Further, as shown in FIG. 2, an entry of each NR in the NRT can contain a plurality of attributes. These attributes include three attributes (i.e., No Remove flag, No HO flag, and No X2 flag) which are controlled by an Operation and Maintenance (OAM) system. The No Remove flag indicates whether or not the eNB can remove the corresponding NR. The No HO flag indicates whether or not the eNB can use the corresponding NR for the purpose of handover. The No X2 flag indicates whether or not the eNB can use the X2 interface (X2 link) in order to initiate a procedure with an eNB that controls a target cell.
In the case of Intra-LTE and Intra-frequency, the ANR function works as follows. The ANR function relies on cells that broadcast their globally unique identifiers (i.e., ECGIs). The serving eNB having the ANR function instructs each UE to perform normal measurements on neighbour cells. Each UE sends a normal measurement report to the serving eNB. This normal measurement report contains PCIs of neighbour cells, but does not contain their ECGIs.
When a measurement report from a UE indicates a new PCI that is not known by the serving eNB, the serving eNB instructs the UE to perform dedicated reporting using the newly found PCI as a parameter. When the UE has found out the new cell corresponding to the newly found PCI, the UE detects system information including the ECGI, Tracking Area Code (TAC), and all available PLMN ID(s), and reports the information to the serving eNB in the dedicated reporting. The TAC indicates a tracking area to which a cell of an eNB belongs. The TAC is a unique identifier within a PLMN and consists of 16 bits.
The serving eNB determines to add, to the NRT, a NR from the source cell to the newly found cell by using the PCI and ECGI which are reported from the UE. The serving eNB may use the PCI and ECGI, which are reported from the UE, to loop up a transport layer address of the eNB controlling the newly found cell. Further, the serving eNB may use the PCI and ECGI to set up an X2 interface (X2 link) with the eNB controlling the newly found cell.